Patients commonly present to the Emergency Department with suspected kidney stone - broadly defined as acute, coliky flank pain radiating to the groin. Patients diagnosed with kidney stones represent 1% of ED visits, accounting for more than one million visits per year. One concerning trend in the evaluation of patients with kidney stones is the increasing utilization of CT scan despite a lack of studies comparing its effectiveness to older, more traditional methods of diagnosis with respect to patient outcomes. In fact, despite a 10-fold increase in CT scan utilization over the years of 1997-2006, there was no change in the rates of diagnosis of kidney stone, serious alternate diagnoses, or hospital admission for kidney stone. On the other hand, there is evidence that CT scans are associated with radiation exposure and increased cost. I propose to derive and validate a decision instrument to identify patients with suspected kidney stone. This decision instrument has the potential to allow emergency physicians to identify patients with suspected kidney stones at very low risk for a serious outcome (alternate diagnoses or complications requiring admission and or surgical intervention), in whom advanced imaging with CT can be deferred. A second concern is the uncertainty regarding the efficacy of medical expulsive therapy for patients with kidney stones. Despite evidence that medical expulsive therapy increases the rate of stone passage in patients diagnosed with kidney stones, a survey of national data from 2006 shows that only 4% of emergency patients receive this therapy. The objectives of this application are two-fold: 1) to improve the diagnostic strategy in patients with suspected kidney stone and 2) to improve the treatment for patients with kidney stones. Aim 1 now focuses on the development of a decision instrument for patients with suspected kidney stone using the rich clinical data already collected as part of the STONE trial. Aim 2 seeks to examine the utilization and outcomes associated with medical expulsive therapy in the STONE trial. We propose to perform an observational study comparing the outcomes including morbidity, health care utilization, and cost in the cohort of patients receiving medical expulsive therapy to the cohort of patients not receiving it. Furthermore, we propose to describe the variation and trends in the utilization of medical expulsive therapy. I anticipate positive impacts in the management of patients with suspected kidney stones after completing these aims. If Aim 1 produces a useful decision instrument, future research could be conducted to broadly validate and determine the impact of these rules and ultimately decrease CT utilization. If Aim 2 confirms the efficacy of MET, I would design implementation studies to translate this finding into clinical care. The experience and training I will derive from completing these aims can then be applied to other emergency department complaints to improve decision making, decrease testing and accelerate the adoption of proven therapies.